Tension rope systems for lifting elevator cars, or similar vessels for vertically raising and lowering loads in industrial or commercial applications, are typically made up of steel ropes. Such ropes typically comprise multiple cords which, in turn, generally comprise a plurality of strands that are made up of individual steel wires. Such tension ropes are critical components upon which safety and productivity often depend.
Deterioration of individual components of a multi-strand or multi-cord rope adversely affects tension strength of the rope. The tension strength of a rope is dependent upon various parameters including its cross-sectional area. When one or more components of a steel rope stretch, tear or permanently bend, those components are disabled or weakened as load bearing members and, thus, the effective tension-bearing cross-sectional area of the rope is reduced. This type of deterioration can occur through a variety of ways, such as normal wear and tear, impact, fatigue or inadvertent corrosion.
Because service ropes, such as elevator ropes, are very long and are made up of many individual wires and strands, it is impractical to perform thorough and accurate testing of rope condition or deterioration level simply by visual inspection. Furthermore, it is impractical to disassemble elevator ropes and apply them to various testing devices. Thus, it is common in the industry to substantially overdesign the ropes to allow for a large margin of deterioration without a large risk of failure. The ropes are replaced at time or cycle milestones. Occasional in-field visual inspections are typically the only means of testing.
The main problem with visual inspection of ropes is that the eye can only see the strands and wires on the outer surface of the rope, which make up only a fraction of the tension-bearing cross-sectional area. Also, it is difficult to visually inspect an entire length of rope installed in, for example, an elevator system. Thus, sampling and approximation methods are generally employed. These methods still require a large margin of overdesign to ensure safety. As a result, ropes are designed with excessive and costly materials, and ropes are often discarded well before their useful life expires. In addition, man hours and operation down-time for inspection are often costly.